1. Field of the Invention
The present invention relates to a method and apparatus for cutting a non-metallic substrate, by which the non-metallic substrate formed of a non-metal material such as glass and silicon is precisely separated into a plurality of small pieces, and more particularly, to a method and apparatus for cutting the non-metallic substrate, in which the non-metallic substrate formed of the glass and the silicon is completely cut using only a scribing laser beam and a breaking laser beam without a cooling device.
2. Description of the Related Art
In recent years, the semiconductor industry, which fabricates a highly-integrated and high-performance semiconductor product, has continued to develop along with a semiconductor thin film processing technique. The semiconductor product has anywhere from a few to a few tens of million semiconductor devices that are integrated on a high-purity substrate called a xe2x80x9cwaferxe2x80x9d that is made of single crystalline silicon, as one of a non-metal material, by the semiconductor thin film processing technique. The semiconductor product serves to store data in digital form or to quickly operate the stored data.
Further, as one of the semiconductor industry applications, a liquid crystal display (LCD) for displaying an analog video signal processed by a data processing unit into digital form has been rapidly developed. In the LCD, liquid crystal is injected between two transparent substrates. A voltage is applied to a certain molecular alignment of the liquid crystal to transform the molecular alignment into that of another. The optical property, such as double refractivity, optical rotary power, dichroism and light scattering, of a liquid crystal cell is changed by the molecular alignment.
The semiconductor product and the LCD have a common feature in that they are formed on a non-metallic substrate, i.e., a high-purity silicon substrate and a glass substrate. Unfortunately, the non-metallic substrate is subject to shock and quite fragile. However, a plurality of semiconductor chips or LCD unit cells are formed on a sheet of wafer or a large-sized glass substrate and then easily separated into each piece.
In the case of the semiconductor product, after forming anywhere from a few to a few hundred semiconductor chips on a sheet of wafer at the same time, and cutting into each chip through a separating process, the semiconductor chip is packaged to produce the semiconductor product.
In the case of the LCD, after forming at least two or more LCD unit cells on the large-sized glass substrate called a motherboard, the LCD unit cell is separated from the motherboard by a separating process, and then they are assembled. At this time, since the separating process occurs during a last step of a production process, a defect in the separating process negatively impacts the productivity and yield of the product. Particularly, the motherboard used for the LCD does not have a crystal structure having the property of glass, the brittleness of the motherboard is lower than that of a silicon wafer. A fine crack is formed at an edge portion of the motherboard during the separating process. The stress is amplified along the crack during a next process used to form the motherboard. Therefore, a defect is easily generated in which an undesired portion of the motherboard is cut.
In the conventional art, a diamond blade, in which a circular plate having a desired diameter is studded with fine diamonds at a circumferential surface thereof and rotated at a high speed, is contacted with a xe2x80x9ccutting pathxe2x80x9d using friction to form a scribe line at a desired depth on a surface of the substrate along the cutting path. Then, a physical impact is applied to the substrate so that a crack is propagated along the scribe line to a lower face of the substrate, thereby separating the semiconductor chip or the LCD unit cell from the wafer or the glass motherboard.
When the wafer or the glass motherboard is separated using the diamond blade, it is necessary to use a cutting margin, which is a desired surface area for the cutting process. Therefore, if the cutting process is not precisely performed, the number of obtained semiconductor chips per a unit wafer decreases due to waste.
Particularly, in the case of the LCD, since a cut face by the diamond blade is roughly formed, many portions on which stresses are concentrated are formed on the cut face. The stress concentration portion of the cut face is easily broken by only a slight impact applied from the outside, so that a crack or a chipping is vertically generated to the cut face.
Further, since the diamond blade generates so many glass particles, an additional cleaning and drying process is required to remove the glass particles. This is disadvantageous to production efficiency.
Recently, to solve the problem, cutting methods using a laser beam have been suggested. For example, U.S. Pat. No. 4,467,168, entitled xe2x80x9cMethod of Cutting Glass with a Laser and an Article Made Therewithxe2x80x9d, U.S. Pat. No. 4,682,003, entitled xe2x80x9cLaser Beam Glass Cuttingxe2x80x9d and U.S. Pat. No. 5,622,540, entitled xe2x80x9cMethod of Breaking a Glass Sheetxe2x80x9d disclose such methods. Since the cutting method using the laser beam is a non-contact type, the vertical crack formed perpendicularly to the cut face is not generated as compared with the cutting method of a contact type using friction with the diamond blade.
FIG. 1 is a view of a conventional laser cutting apparatus for cutting a glass substrate using a laser beam.
As shown in FIG. 1 a scribing laser beam 13, for example a CO2 laser beam having an absorptivity of 95% or more with respect to the glass, is scanned along a cutting path 12 formed on a glass motherboard 10 so as to rapidly heat the cutting path 12 of the motherboard 10.
Then, a cooling fluid beam 14 having a markedly lower temperature than the heating temperature of the glass motherboard 10 is applied onto the rapidly heated cutting path 12. Accordingly, while the glass motherboard 10 is rapidly cooled, a crack is generated on a surface of the motherboard 10 to a desired depth to generate a scribe line 15. Also, the cooling fluid beam 14 may be positioned to be apart from the scribing laser beam 13 at a desired distance or to be adjacent to the scribing laser beam 13. Otherwise, the cooling fluid beam 14 may be positioned at an inner portion of the scribing laser beam 13.
Subsequently, a breaking laser beam 16, such as the CO2 laser beam, is linearly scanned along the scribe line 15 so as to heat the scribe line 15 rapidly. Thus, a strong tensile force is generated at the scribe line 15 in the direction shown in FIG. 1, so that the glass motherboard 10 is completely cut off along the scribe line 15. Meanwhile, the breaking laser beam 16 is symmetrically applied with respect to the scribe line 15 to heat both sides of the scribe line 15 rapidly.
The conventional laser cutting apparatus, as described above, is mainly comprised of a laser beam generating portion and a cooling portion so as to heat a non-metallic substrate, such as the glass having a low thermal conductivity, using the laser beam and then rapidly cool the heated portion of the non-metallic substrate. Therefore, a thermal stress is propagated to a heat moving direction, so that the substrate is cut.
However, in the conventional laser cutting apparatus, the substrate has to be cooled rapidly, using a cooling material in gaseous or liquid state, after being scanned by the scribing laser in order to induce sudden temperature changes. This limits the cutting speed of the substrate.
In order to out the glass such as Borosilicate glass (BSG) having a thermal conductivity of 0.26 kcal/mhxc2x0 C. (the thermal conductivity of metal is 57 kcal/mhxc2x0 C.), the laser beam should be condensed. However, since laser beam energy applied to each unit surface area is inversely proportional to the cutting speed, increasing the cutting speed causes the laser beam energy applied to each unit surface area to be lowered, even if the laser beam is condensed. Therefore, the substrate may not be fully cut. Accordingly, the cutting method using the high harmonics laser beam is inferior with respect to the cutting speed as compared with the conventional mechanical cutting method that controls the cutting speed by increasing a mechanical speed.
Further, since the propagating method of the thermal stress has to generate a micro-crack at an early stage of the cutting process, an initial crack should be generated at an initial cutting point by a physical force using the scribing laser beam such as the CO2 laser beam, or by a laser beam based on an impact energy such as YAG. Therefore, a fabricating cost is disadvantageously increased, because the laser cutting apparatus has total three laser generating portions, to include the laser for generating the initial crack, the scribing laser and the breaking laser. Moreover, if a laser head is moved by a repeat operation of the cutting equipment, the initial crack is inconsistent with the scribe line. Therefore, the cutting process has a defect in that a cut line is irregularly formed at a starting portion of the substrate.
In addition, in the conventional cutting method using the laser beam described above, since the cooling material such as water, dry ice, helium gas, etc., is positively necessary, a contamination caused by the coolant may cause a problem. That is, when the glass motherboard in which a cut piece is used in the LCD, the remaining coolant is introduced to a liquid crystal injecting port after the cutting operation, thereby generating a defect in a liquid crystal injecting process. Therefore, a further process is essentially required to remove the remaining cooling material after completing the cutting operation. Moreover, if gas is used as the cooling material, since the gas has a lower density than a liquid material, the gas should have a lower temperature than a liquid cooling material to increase cooling efficiency. However, if the gas temperature is lower than the ambient temperature, it quickly lowers the ambient temperature during the cutting operation, condensing the moisture around. This moisture causes defects in the cutting process.
Therefore, it is an object of the present invention to provide a method of cutting a non-metallic substrate made of glass or silicon, in which the non-metallic substrate is completely cut by using only a scribing laser beam and a breaking laser beam without a cooling device.
It is another object of the present invention to provide an apparatus for cutting a non-metallic substrate, which properly performs the cutting method.
To achieve the aforementioned objects of the present invention, there is provided a method of cutting a non-metallic substrate, which comprises the steps of scanning a first laser beam for breaking bonds between molecules of the non-metallic substrate material on a cutting path formed on the non-metallic substrate to form a scribe line having a crack to a desired depth, and scanning a second laser beam along a scanning path of the first laser beam to propagate the crack in a depth direction of the substrate and to completely separate the non-metallic substrate.
To achieve another object of the present invention, there is provided an apparatus for cutting a non-metallic substrate, which comprises a first laser beam generating means, which generates a first laser beam for breaking bonds between molecules of the non-metallic substrate material so as to heat a cutting path formed on the non-metallic substrate and to form a scribe line having a crack to a desired depth, and a second laser beam generating means, which generates a second laser beam for propagating the crack along a scanning path of the first laser beam in a depth direction of the substrate.
According to the present invention as described above, the first laser beam having a wavelength identical with a natural frequency of the non-metallic substrate is used for breaking the molecular bonds of the non-metallic substrate. A scribe line having a narrow and deep crack is formed on the cutting path of the non-metallic substrate, for example a glass, by the first laser beam, e.g., the 4th harmonic yttrium aluminum garnet (YAG) laser beam having a wavelength of 266 nm and an absorptivity of 90% and more with respect to the non-metallic substrate. Then, the CO2 laser beam as the second laser beam is scanned onto the scribe line to propagate the crack in the depth direction of the substrate and to completely cut the non-metallic substrate.
Accordingly, the cutting apparatus has only a scribing laser (the first laser) and a breaking laser (the second laser) without the cooling device, thereby simplifying a structure thereof and reducing the fabricating cost in comparison with a conventional one.
Further, since a cutting speed can be controlled by a speed of the first laser beam, the cutting speed can be increased and controlled with ease as compared with the conventional cutting method using the temperature difference due to the heating and the cooling operation.
Moreover, the cooling device is not employed in the cutting apparatus of an embodiment of the present invention, thereby preventing the process defect such as the contamination of the liquid crystal injecting port after the cutting operation.